On this page7 sections
A sour service valve line, in short:
- Name the document, its part for each material, and its edition.
- Send the service conditions the end user has set.
- Say which valve parts and documents the requirement covers.
The full enquiry checklist is further down. Already have the datasheet? Send it with the end user's specification to enquiry@flowsynergy.ae for valve selection and technical support.
What is NACE MR0175 / ISO 15156?
NACE MR0175 / ISO 15156 is the materials standard for equipment in oil and gas production and gas treatment plants where hydrogen sulfide (H2S) is present. It sets out how metallic materials are selected and qualified to resist the cracking H2S can cause, where a failure could put people or the environment at risk.
The two names are one document. TWI writes that "NACE MR0175 has been entirely replaced by the International Standard ISO15156-1 to ISO15156-3 issued in 2003 with subsequent editions". The text is identical wherever it is issued; only in the USA does the MR0175 label stay on the cover, because certain US state laws require compliance with NACE MR0175. NACE, now AMPP, supported the move, and the standard is maintained via AMPP and ISO.
The standard has three parts. Part 1 sets the general principles. Part 2 covers carbon and low-alloy steels, and its Annex A lists the carbon and low alloy steels accepted as resistant to sulfide stress cracking. Part 3 covers corrosion-resistant alloys (CRAs) and other alloys. All three are the fourth edition, published on 17 November 2020, and each record lists a final draft (ISO/FDIS) revision. The material limits themselves sit in the licensed standard and in the project specification, not on this page. Our glossary entry gives the short definition.
What does ISO 15156 cover, and what does it leave out?
ISO 15156 deals with the cracking that hydrogen sulfide can cause in metal, and Parts 2 and 3 say they do not address corrosion. So a valve material chosen to ISO 15156 is chosen against cracking; whether it also resists general or localized corrosion in the same line is a separate decision, and the valve still needs its own design standard.
The Part 1 record lists the cracking mechanisms: sulfide stress cracking (SSC), stress corrosion cracking (SCC), hydrogen-induced cracking (HIC) and stepwise cracking (SWC), stress-oriented hydrogen-induced cracking (SOHIC), soft zone cracking (SZC), and galvanically induced hydrogen stress cracking (GHSC).
Parts 2 and 3 state that the document "is concerned only with cracking. Loss of material by general (mass loss) or localized corrosion is not addressed." So a valve material that meets ISO 15156 can still corrode, and a corrosion allowance or a more resistant alloy is a separate choice. Our guide to super duplex valve materials for seawater works through one such choice.
Part 1 also says it "supplements, but does not replace, the materials requirements given in the appropriate design codes, standards, or regulations". The valve still needs its own design and rating standard, for example ASME B16.34 for pressure-temperature ratings.
| Part | Materials | Cracking addressed | Stated limit |
|---|---|---|---|
| ISO 15156-1 | General principles for metallic materials | All mechanisms H2S can cause | Supplements design codes, does not replace them |
| ISO 15156-2 | Carbon and low-alloy steels; Annex A lists SSC-resistant grades | Sulfide stress cracking, SOHIC, soft zone cracking, HIC and stepwise cracking | Cracking only, not mass loss or localized corrosion |
| ISO 15156-3 | Corrosion-resistant alloys and other alloys | Sulfide stress cracking, stress corrosion cracking and GHSC | Cracking only, not mass loss or localized corrosion |
Production or refinery: MR0175 or MR0103?
Production and gas treatment plants use ISO 15156 (NACE MR0175). Refinery sour service uses NACE MR0103, and ISO 17945 covers sulfide stress cracking in sour refining environments. The Part 1 record says ISO 15156 "is not necessarily applicable to equipment used in refining or downstream processes and equipment", so check which document your specification names. TWI puts it plainly: "For applications in refineries, then NACE MR0103 is the appropriate standard".
The split goes back decades. In a CORROSION/2004 paper, Don Bush of Emerson's Fisher Controls, Jeff Brown of Motiva and Keith Lewis of Shell record that NACE issued MR0175 in 1975, and that its scope "includes only oilfield equipment and associated facilities (including gas production and treatment)". Refineries had used it anyway, "even though refinery applications were outside the scope of MR0175".
Writing in 2004, the same authors say MR0103 borrowed MR0175's alloy grouping "but did not implement environmental limits such as H2S partial pressures, temperature limits, pH restrictions, etc." They also note that the late-1990s rewrite of MR0175 proposed taking in chloride stress corrosion cracking, because "most oil and gas production streams contain chlorides in sufficient levels to cause SCC in susceptible alloys", while in refineries chloride levels "tend to be low enough that chloride SCC isn't a common concern".
| Question | ISO 15156 (NACE MR0175) | ISO 17945 (sour refining) |
|---|---|---|
| Where it applies | Oil and gas production, natural-gas sweetening and treatment plants | Sour petroleum refining and related processing environments |
| Cracking covered | All mechanisms H2S can cause | Sulfide stress cracking; other wet H2S cracking outside its scope |
| Equipment | Listed in the standard's own Table 1 (not reproduced here) | Valve bodies, among other equipment |
| Design specifications | Supplements design codes | Does not include design specifications |
| Edition on the record | Fourth edition, 17 November 2020; a final draft revision is listed | First edition, 13 April 2015 |
Who decides that a valve line is sour?
The end user decides whether a valve line is sour, through the project's own specification. A supplier reads the line conditions but does not set them. So a sour line should arrive with its service conditions, not only the word "NACE". TWI writes that "The emphasis now is clearly on the end user to determine what is acceptable for their service requirements and it also allows relaxation for some conditions."
The conditions that decide which materials are acceptable come from the process. Hydrogen sulfide level, temperature and pH are the environmental limits the CORROSION/2004 authors say MR0103 did not adopt from MR0175; chlorides matter mainly in production streams. Our guide to valve selection by service condition shows how the same line data drives the rest of the valve.
Welds need a word too. TWI notes that ISO 15156 brought "requirements to test the hardness of welds with Vickers 5 or 10kg load". A welded or overlaid valve body should say how its weld hardness was tested, and the inspection documents should carry it.
What should a sour service valve enquiry state?
A sour service valve enquiry should name the document, the part for each material and the edition, send the end user's service conditions, and say which valve parts and documents the requirement covers. Without those, two quotations "to NACE" can rest on different documents. Flowsynergy supplies ball, gate, globe, check and butterfly valves across the UAE and the Gulf from Level 41, Emirates Towers, Dubai, with valve selection and technical support.
- The document, part and edition for each material: ISO 15156-2:2020 for carbon and low-alloy steel parts and ISO 15156-3:2020 for CRA parts, or NACE MR0103 or ISO 17945 for a refinery.
- The service conditions the end user has set for the line.
- Valve type, size, class and ends. Our guide to valve selection covers the rest of the line.
- Which parts the requirement covers: body, bonnet, trim, stem and bolting, as the specification states.
- For welded or overlaid parts, how weld hardness is to be tested.
- The documents: a material statement against the named part, and the certificate type. See our guide to MTCs and test certificates.
Pricing a sour line? Call +971 4 313 2786, email enquiry@flowsynergy.ae or use the enquiry form, Monday to Friday, 8:30 am to 5:00 pm, Dubai time.
What else do buyers ask about sour service valves?
Are NACE MR0175 and ISO 15156 the same document?
Yes. TWI writes that MR0175 "has been entirely replaced" by ISO 15156 Parts 1 to 3, and that the text is identical in all documents issued by individual standards authorities. The double label is kept in the USA because certain US state laws require compliance with NACE MR0175.
What does "NACE compliant" mean on a valve quotation?
It is the maker's statement that named materials meet a named part and edition of ISO 15156, or of NACE MR0103 for a refinery. Ask which part and edition, which valve parts it covers, and how weld hardness was tested, and see it in the documents.
Does an ISO 15156 material resist corrosion too?
Not on the strength of ISO 15156. Parts 2 and 3 say they are concerned only with cracking and that general or localized corrosion is not addressed. Corrosion resistance in the same line is chosen separately, for example with a corrosion allowance or a more resistant alloy.
Which edition of ISO 15156 is current?
On the Standard Norge records read for this guide on 21 October 2026, the latest published parts are the fourth edition of 17 November 2020, and each record lists a final draft (ISO/FDIS) revision. Confirm the edition your specification names before ordering, because a new edition would replace it.
Sources quoted on this page
- Standard Norge catalogue records for ISO 15156-1:2020, ISO 15156-2:2020 and ISO 15156-3:2020, fourth edition, 17 November 2020: their scope abstracts.
- Standard Norge catalogue record for ISO 17945:2015, published 13 April 2015: its scope abstract.
- TWI, "What has happened to the MR0175 standard for sour service in exploration and production applications and what is ISO15156?", read 21 October 2026.
- Don Bush (Emerson Process Management / Fisher Controls), Jeff Brown (Motiva Enterprises) and Keith Lewis (Shell Global Solutions), "An Overview of NACE International Standard MR0103 and Comparison with MR0175", CORROSION/2004 paper 04649.
Scope details are summarised from public catalogue records; no clause, table or limit from ISO 15156, ISO 17945, NACE MR0175 or NACE MR0103 is reproduced. Reference data only, not a claim that Flowsynergy stocks, tests or is accredited to any of these standards: confirm every line against the current edition.